This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The simultaneous acquisition of x-ray diffraction data and single crystal absorption spectra in the UV/Visible region was explored at near liguid helium temperatures. A single crystal microspectrophotometer was set up on BL12-2 to record spectra ?in-situ? from crystals mounted on the goniometer. The conventional liquid nitrogen cold stream was replaced by a liquie helium coldstream system. During diffraction experiments, spectroscopic measurements were analyzed to confirm the redox state of the metal site of the enzyme crystal. Rates of radiation-induced photo-reduction were measured at 80 K and ~15 K. Based on these measurements, the rate of reduction was reduced by a factor of 2-3 at the lower temperature.